It does appear to be on B. From the previous experiment it also seems to be on main3, so I think main3 should also be phase B and by elimination, main2 should probably be phase C.
With the mains properly labeled, you may be able to determine which main is associated with each of the remaining circuits, and assign them to the same phase as their associated main. This is where you may find that the various feeds to shed, garage, and AC are color coded by phase.
Of particular interest will be the solar, because the main associated with that should have “allow negative values” checked so that it can properly track exported power.